Thickener for surface active agent and detergent composition

There are provided a thickener used in surfactant, which shows excellent effect of thickening to surfactant, which is especially effective in thickening anion surfactants of acyl amine acidic type or amphoteric surfactant of alkyl iminodicarboxylate type, and the composition of detergent with excellent bubble quality, which contains the said thickener and without feeling slick. The resolution is that there is provided a thickener used in surfactant, which is presented by the following formula (1): R1O(EO)x(BO)y(EO)zH (1) (In formula, R1 represents the group with 8-14 carbons selected from alkyl group, alkenyl group, and acyl group; EO represents ethylene oxide group; BO represents butylene oxide group; then x, y, and z individually represent average adductive moles, and 0≤x≤3, 1≤y≤3, 0≤z≤3, and 0≤x+z≤3.)